During the construction of an underground concrete diaphragm wall or an in-situ concrete pile, it is very important to be able to ascertain details of a wall surface condition which is stabilized using liquid, in the form of visual images for maintaining the quality of construction as well as for safety purposes. In this connection measuring devices which utilize ultrasonic waves have been both disclosed and put into practical application. Examples of these methods are disclosed in Japanese Patent Application No. 49-5726 (Registered Patent No. 1059047), No. 50-14961 (Registered Patent No. 1119189) and No. 55-7525.
The above-mentioned conventional measuring devices which utilize ultrasonic waves, however, can only achieve two-dimensional measuring of, so to speak, vertical sections of a deep trench or a deep hole and enable a two-dimensional visualization of the wall configuration, inclination and surface irregularity, and cannot provide three-dimensional surface information. Further, conventional measuring devices cannot provide information relating to the quality of the surface which reflects the ultrasonic waves (the kind of stratum, for example, that constitutes the wall surface) and hence cannot indicate if an irregularity of the surface is caused by clay being swelled by water or by mechanical deformation. Thus, these devices are quite inadequate as measuring devices and cannot provide the information necessary for judgments which are essential for maintaining construction quality and necessary safety levels.